5.3 Sympathomimetics, Cocaine, Amphetamines, Synthetic Cannabinoids, and Hallucinogens

Substances of abuse and psychostimulants account for a substantial volume of acute emergency department consultations managed by poison control centers. These xenobiotics span diverse pharmacological classes—naturally occurring plant alkaloids (cocaine), synthetic and substituted phenethylamines (amphetamines, methamphetamine, MDMA), synthetic cathinones ("bath salts"), high-affinity synthetic cannabinoid receptor agonists, dissociative arylcyclohexylamines (phencyclidine, ketamine), classic indolealkylamine hallucinogens, and veterinary adulterants (xylazine). Despite disparate molecular structures, stimulants share a common clinical endpoint: massive hyperactivation of central and peripheral monoaminergic neurotransmission, provoking life-threatening cardiovascular, hyperthermic, metabolic, and behavioral crises.

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The Sympathomimetic Toxidrome and Differential Diagnosis

Under physiological conditions, endogenous catecholamines (norepinephrine, epinephrine, dopamine) stimulate adrenergic receptor subtypes: alpha-1 (vascular smooth muscle vasoconstriction, mydriasis), alpha-2 (presynaptic inhibition of norepinephrine release), beta-1 (positive inotropy, chronotropy, dromotropy), and beta-2 (bronchodilation, peripheral vasodilation, tremor, glycogenolysis, and potassium influx). In stimulant toxicity, unregulated sympathetic outflow saturates these receptors, creating the classic sympathomimetic toxidrome.

Clinical Manifestations of the Sympathomimetic Toxidrome

• Vital Signs: Tachycardia (sinus tachycardia, supraventricular tachycardias), profound hypertension, tachypnea, and hyperthermia (often >40°C in severe cases).
• Physical Examination: Dilated pupils (mydriasis with reactive light reflex), profuse diaphoresis (skin is hot, flushed, and noticeably wet), tremors, hyperreflexia, and hyperactive bowel sounds.
• Neuropsychiatric Examination: Psychomotor agitation, hypervigilance, paranoia, visual/tactile hallucinations ("formication" or cocaine bugs), delirium, and violent impulsivity.

Critical Differential Diagnosis: "Wet vs. Dry"

The single most critical diagnostic distinction in acute emergency toxicology is differentiating the sympathomimetic toxidrome from the anticholinergic (antimuscarinic) toxidrome. Both syndromes present with tachycardia, hypertension, hyperthermia, mydriasis, and delirium. However, their physical examination findings diverge sharply based on sweat gland innervation:

Sympathomimetic Toxicity:   Sympathetic Cholinergic Sweat Glands Activated (Muscarinic M3) → PROFUSE DIAPHORESIS (Wet)
Anticholinergic Toxicity:    Muscarinic M3 Blockade on Sweat Glands → ANHIDROSIS & DRY MUCOUS MEMBRANES (Dry)

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Cocaine: Triple Reuptake Inhibition, Cardiotoxicity, and Chest Pain Controversies

Cocaine (benzoylmethylecgonine), an alkaloid derived from Erythroxylum coca, is unique among recreational psychostimulants because it combines potent monoamine reuptake inhibition with potent local anesthetic membrane-stabilizing activity.

Multi-Receptor Mechanisms of Toxicity

1. Presynaptic Monoamine Reuptake Blockade: Cocaine competitively binds and blocks presynaptic transporters: the norepinephrine transporter (NET), dopamine transporter (DAT), and serotonin transporter (SERT). By preventing reuptake, massive concentrations of monoamines accumulate in the synaptic cleft, driving peripheral vasoconstriction, severe hypertension, tachycardia, and intense central euphoria/addiction.
2. Myocardial Fast Sodium Channel Blockade (Nav1.5): Similar to Class IC antiarrhythmics and tricyclic antidepressants, cocaine directly binds voltage-gated fast inward sodium channels in cardiac tissue. By slowing Phase 0 action potential depolarization, cocaine delays intraventricular conduction, manifesting on the 12-lead ECG as widening of the QRS complex (>100 ms), negative inotropy, and monomorphic ventricular tachycardia. Hypertonic sodium bicarbonate (1-2 mEq/kg IV push) is the specific treatment for cocaine-induced QRS prolongation.
3. Potassium Channel Blockade: Cocaine inhibits the cardiac outward potassium current (IKr), prolonging Phase 3 repolarization and the QT interval, predisposing to early afterdepolarizations and polymorphic ventricular tachycardia.
4. Endothelial Injury and Thrombogenesis: Cocaine stimulates the release of endothelin-1, suppresses nitric oxide production, and activates platelets to release thromboxane A2, promoting acute intravascular platelet aggregation, coronary thrombosis, and aortic dissection.

The Beta-Blocker Controversy and Unopposed Alpha Stimulation

Cocaine-associated chest pain accounts for hundreds of thousands of emergency department evaluations annually. The management hierarchy is distinct from standard acute coronary syndrome (ACS):

Cocaine Ingestion → Massive Presynaptic Release of Norepinephrine & Epinephrine
                                       ↓
         [Vasoconstriction via Alpha-1]  +  [Vasodilation via Beta-2]
                                       ↓
             Administering Pure Beta-Blocker (e.g., Metoprolol, Propranolol)
                                       ↓
                  Selectively Abolishes Beta-2 Vasodilation
                                       ↓
                 UNOPPOSED ALPHA-1 ADRENERGIC STIMULATION
                                       ↓
Severe Paradoxical Coronary Artery Vasospasm + Malignant Systemic Hypertension + Myocardial Infarction

• The Mechanism of Unopposed Alpha-Stimulation: Vascular smooth muscle tone reflects a dynamic balance between vasoconstrictor alpha-1 receptors and vasodilatory beta-2 receptors. In severe cocaine toxicity, both receptor populations are heavily stimulated by massive catecholamine surges. If a pure or selective beta-blocker (e.g., metoprolol, propranolol, atenolol, esmolol) is administered, the vasodilatory beta-2 counterbalance is eliminated. Circulating catecholamines act exclusively on unblocked alpha-1 receptors, precipitating severe paradoxical coronary artery spasm, malignant systemic hypertension, myocardial ischemia, and death.
• The Role of Labetalol and Carvedilol: While labetalol is often cited as a mixed alpha/beta-blocker, its IV formulation possesses an alpha-to-beta blockade ratio of only 1:7 (predominantly beta). Clinical studies have demonstrated that labetalol does not consistently alleviate cocaine-induced coronary vasoconstriction and can worsen hemodynamics; standard clinical toxicology guidelines caution against its use in acute cocaine toxicity.

Management Hierarchy for Cocaine-Induced Chest Pain

1. Intravenous Benzodiazepines (First-Line): Administer Lorazepam (2 to 4 mg IV) or Diazepam (5 to 10 mg IV) every 5 to 10 minutes until agitation, tachycardia, and hypertension resolve. Benzodiazepines enhance central GABA-A tone, blunting central sympathetic outflow, reducing heart rate, blood pressure, and myocardial oxygen demand, while relieving coronary spasm.
2. Nitrates and Dihydropyridine Calcium Channel Blockers: Sublingual or IV nitroglycerin or IV nicardipine directly reverse coronary vasospasm and decrease left ventricular afterload.
3. Direct Alpha-Antagonists for Refractory Vasospasm: If severe hypertension and coronary spasm persist despite maximal benzodiazepines and nitrates, administer phentolamine (1 to 5 mg IV), a competitive alpha-1/alpha-2-adrenergic antagonist.
4. Sodium Bicarbonate for Conduction Delays: If the ECG displays a QRS duration > 100 ms or wide-complex tachycardia, administer 8.4% sodium bicarbonate (1 to 2 mEq/kg IV push) to overcome fast sodium channel blockade.

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Amphetamines, Methamphetamine, and Synthetic Cathinones

Substituted amphetamines—including dextroamphetamine, methamphetamine, and synthetic cathinones ("bath salts")—exert stimulant actions through mechanisms distinct from cocaine.

Molecular Mechanisms: Substrates and Reverse Transport

Unlike cocaine (which merely blocks the external reuptake pore), amphetamines act as substrates for monoamine transporters:

1. Amphetamines are transported into the presynaptic cytoplasm via DAT, NET, and SERT.
2. Once inside the terminal, amphetamines enter storage vesicles via the vesicular monoamine transporter 2 (VMAT2), disrupting the intravesicular acidic pH gradient.
3. This collapses the vesicular storage capacity, releasing free dopamine and norepinephrine into the presynaptic cytoplasm.
4. Elevated cytosolic monoamines reverse the direction of DAT and NET, actively pumping massive surges of catecholamines out of the cell into the synaptic cleft.
5. Amphetamines also inhibit monoamine oxidase (MAO), blocking intracellular enzymatic degradation.

Lethal Hyperthermia, Rhabdomyolysis, and Renal Failure

Methamphetamine and synthetic cathinones frequently precipitate catastrophic exertional/hyperactive hyperthermia (core body temperature > 40°C to 42°C / 104°F to 107.6°F). This hyperthermia results from a dual etiology: intense muscular hyperactivity (incessant agitation, violent struggling, pacing) combined with direct catecholamine-induced uncoupling of oxidative phosphorylation in skeletal muscle mitochondria.

• Pathophysiology: Core temperatures above 40°C denature cellular proteins, destroy endothelial integrity, provoke widespread disseminated intravascular coagulation (DIC), trigger systemic inflammatory response syndrome (SIRS), and cause irreversible cerebellar Purkinje cell necrosis.
• Rhabdomyolysis: Intense muscle rigidity and agitation cause ischemic skeletal muscle necrosis. Myocytes rupture, releasing massive amounts of potassium, phosphate, and myoglobin into the bloodstream. Serum creatine kinase (CK) levels commonly surge to 20,000 to > 100,000 IU/L. In the acidic renal tubular lumen, myoglobin precipitates with Tamm-Horsfall proteins, forming obstructing casts, while generating toxic free iron radicals that cause lipid peroxidation and acute tubular necrosis (ATN).
• Treatment Protocol:
  1. Immediate Rapid Active Cooling: Antipyretics (acetaminophen, ibuprofen) are completely ineffective because hyperthermia is driven by peripheral muscular work, not an altered hypothalamic set-point. The patient must be immediately cooled using ice-water immersion or evaporative cooling (continuous misting with tepid water while high-flow fans circulate air) to reduce core temperature below 39°C within 20 to 30 minutes.
  2. Aggressive IV Benzodiazepine Sedation: High-dose IV lorazepam or diazepam must be administered to abolish shivering, agitation, and skeletal muscle rigidity.
  3. Volume Resuscitation: Administer isotonic crystalloids (normal saline or lactated Ringer's) at 200 to 500 mL/hr to maintain a target urine output of 1.5 to 2.0 mL/kg/hour, preventing myoglobin precipitation in renal tubules.

Synthetic Cathinones ("Bath Salts") and Hyperactive Delirium

Synthetic cathinones—such as methylenedioxypyrovalerone (MDPV), mephedrone, and alpha-pyrrolidinopentiophenone (alpha-PVP / "Flakka")—are beta-keto amphetamine analogues. They exhibit ultra-high potency at DAT and prolonged half-lives, often producing protracted hyperactive delirium with severe agitation (a presentation previously labeled "excited delirium," a term professional societies now discourage):

• Extreme psychomotor agitation, profound paranoia, bizarre violent behavior, hyperthermia, superhuman perceived strength, and complete imperviousness to physical pain.
• Patients frequently suffer sudden cardiac arrest following physical struggle against police or medical restraints due to profound metabolic acidosis, catecholamine surge, hyperkalemia from rhabdomyolysis, and autonomic collapse.
• Management demands rapid neurochemical control using IV benzodiazepines, rapid physical cooling, and rapid correction of acidosis.

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MDMA (Ecstasy / Molly): SIADH and Hyponatremic Encephalopathy

MDMA (3,4-methylenedioxymethamphetamine) possesses a unique pharmacological profile: it binds preferentially to the serotonin transporter (SERT), promoting massive synaptic serotonin release alongside moderate dopamine and norepinephrine release. This produces feelings of intense empathy, euphoria, and sensory enhancement.

The Hyponatremia Disaster: Drug-Induced SIADH plus Water Intoxication

While hyperthermia and serotonin syndrome are well-recognized risks of MDMA, its most distinctive, life-threatening metabolic emergency is acute severe hyponatremic encephalopathy.

MDMA Ingestion → Serotonin (5-HT2A) & Alpha-1 Stimulation in Hypothalamus
                                       ↓
         Non-Osmotic Release of Arginine Vasopressin (AVP / ADH) → Drug-Induced SIADH
                                       ↓
      Renal V2 Receptors Activated → Water Retention & Inability to Excrete Free Water
                                       ↓
      User Experiences Thirst & Follows Rave Advice: Ingests Copious Plain Water
                                       ↓
   ACUTE SEVERE HYPONATREMIA (Serum Na+ < 115-120 mEq/L) within 2-6 Hours
                                       ↓
   Rapid Osmotic Brain Swelling → Cerebral Edema → Seizures → Transtentorial / Uncal Herniation

1. Drug-Induced SIADH: MDMA and its primary metabolite, HMMA, stimulate the hypothalamus to release large quantities of arginine vasopressin (AVP / antidiuretic hormone) via 5-HT2A and alpha-1 pathways, independent of serum osmolality. This halts free water excretion in the renal collecting ducts.
2. Hypotonic Fluid Overload: At electronic dance festivals or raves, users are heavily counseled to drink water to prevent dehydration. Compounding this, MDMA stimulates central thirst. Users consume liters of plain water or low-solute beverages.
3. Rapid Cerebral Edema: Within hours, serum sodium plummets, frequently dropping below 115 to 120 mEq/L. Because the drop occurs acutely (<48 hours), the brain cannot synthesize idiogenic osmoles to compensate. Free water shifts rapidly into brain astrocytes, producing fulminant cerebral edema, obtundation, status epilepticus, uncal/transtentorial herniation, and death. Young females are at disproportionate risk due to estrogen-mediated inhibition of the cerebral astrocytic Na+/K+-ATPase pump.

Management of MDMA Hyponatremic Encephalopathy

• Hypertonic Saline (3% NaCl) Bolus: In any MDMA user who presents with seizures, coma, or signs of herniation, immediately administer 100 mL of 3% Hypertonic Saline IV over 10 minutes. This bolus may be repeated twice every 10 to 15 minutes (up to a total of 300 mL) until active seizures cease.
• Target Sodium Elevation: The goal of acute emergency therapy is to rapidly raise serum sodium by 3 to 5 mEq/L, which is sufficient to reverse acute brain swelling and arrest herniation without risking osmotic demyelination syndrome.
• Fluid Restriction: All hypotonic and isotonic maintenance IV fluids must be discontinued immediately.

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Hallucinogens, Dissociatives, Synthetic Cannabinoids, and Adulterants

Phencyclidine (PCP): The Multi-Directional Nystagmus Hallmark

Phencyclidine is an arylcyclohexylamine that blocks the open channel pore of the N-methyl-D-aspartate (NMDA) glutamate receptor, while inhibiting dopamine, norepinephrine, and serotonin reuptake. The hallmark physical finding is multidirectional nystagmus—the presence of rotary nystagmus combined with horizontal and vertical nystagmus. Patients display alternating behavioral states, abruptly transitioning from motionless catatonia with a blank stare to explosive, violent agitation. Because PCP produces profound sensory dissociation and analgesia, patients frequently cause severe physical trauma to themselves (fractures, self-inflicted wounds) without experiencing pain.

Xylazine ("Tranq"): The Emerging Alpha-2 Threat

Xylazine is a non-opioid veterinary tranquilizer frequently co-mixed with illicit fentanyl. Acting as a potent central alpha-2-adrenergic agonist (pharmacologically similar to clonidine), it suppresses central sympathetic outflow. Patients present with deep coma, severe bradycardia, hypotension, and miosis. While naloxone reverses the co-administered opioid and restores spontaneous respiration, naloxone does NOT reverse xylazine. Furthermore, chronic xylazine use induces extensive, painful necrotic cutaneous ulcerations (often developing at anatomic sites distant from injection sites), requiring extensive wound debridement and supportive care.

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Clinical Poison Center Case Scenario: The Collapsed Festival Attendee

A 19-year-old female is rushed to the festival medical tent after collapsing during a summer electronic music festival. Witnesses report she consumed two "Molly" tablets 4 hours earlier and had been continuously dancing while drinking large quantities of water from a hydration backpack. She suddenly developed a generalized tonic-clonic seizure lasting 4 minutes. On arrival, she is unresponsive (GCS 5), with a blood pressure of 144/92 mmHg, heart rate of 118 bpm, core temperature of 38.8°C (101.8°F), and bilateral dilated reactive pupils. While the medical team is preparing IV lorazepam, a bedside point-of-care electrolyte panel reveals a serum sodium concentration of 114 mEq/L.

Poison Specialist Consultation and Interventions

1. Diagnostic Synthesis: The patient has acute MDMA-induced hyponatremic encephalopathy resulting from non-osmotic AVP release (SIADH) combined with massive hypotonic water ingestion. Her status epilepticus and coma reflect acute cerebral edema with imminent risk of uncal herniation.
2. Definitive Treatment: The poison specialist advises the immediate administration of 100 mL of 3% Hypertonic Saline IV over 10 minutes, rather than relying solely on benzodiazepines. Normal saline (0.9%) is strictly avoided because its osmolality (~308 mOsm/L) can act as free water in a patient with elevated urine osmolality from SIADH.
3. Clinical Course: Ten minutes after the 3% saline infusion, her seizure activity ceases completely. A second 100-mL bolus is administered. Repeat serum sodium increases to 119 mEq/L. The patient begins localizing to pain, avoids endotracheal intubation, and recovers fully with strict fluid restriction in the intensive care unit.